The present invention generally relates to a vehicle steering system and, more particularly, to a vehicle steer-by-wire steering system providing road wheel force feedback to the hand-operated steering wheel.
Land vehicles are commonly equipped with a set of road wheels that rotate to allow easy movement of the vehicle. Automotive vehicles are conventionally equipped with a pair of front wheels that are controllably steerable to enable the vehicle to turn left and right as it maneuvers on land. In the past, vehicle steering systems commonly employed a direct mechanical connection between the hand-operated steering wheel and the steerable wheels, which typically included the front two wheels, of an automotive vehicle. As an operator rotated the hand-operated steering wheel, a mechanical linkage through the vehicle's tie-rods actuated the steerable road wheels in either the left or right direction, generally with the assistance of a power-assisted steering motor.
Recently, steer-by-wire steering systems have been introduced into automotive vehicles to provide easy-to-steer road wheel control. Included in a typical steer-by-wire steering system is a steering wheel subassembly for monitoring the angular position of the steering wheel, wheel actuation controllers, and corresponding electric motor actuators for controlling actuation of the individual wheels. The steer-by-wire steering system turns the road wheels left and right with the motor actuators which in turn are controlled by controllers in response to tracking the sensed position of the steering wheel. In contrast to prior steering systems, the steer-by-wire steering system does not employ a mechanical linkage between the steering wheel and the individual steerable wheels. For safety and reliability, the steer-by-wire steering system generally employs redundant steering wheel sensors, redundant controllers, and redundant motor actuators.
In the conventional steer-by-wire vehicle steering system, torque sensors are generally employed to sense forces which deflect the steerable road wheels, such as when a vehicle road wheel forcibly contacts a roadside curb or other opposing object. The torque sensor signals are read by a local controller and sent to a hand wheel controller via a bus. The hand wheel controller uses the torque signals to actuate the hand wheel motor to provide rotational resistance such that the operator of the vehicle may feel resistance to turning the road wheel. However, the use of torque sensors adds additional components to the steering system, which increases the cost, as well as requires low noise signal conditioning circuitry and hardware/software compensation to correct for non-linearity of the torque sensors. Further, torque sensors are generally susceptible to error due to drift over temperature and often require calibration.
Accordingly, it is therefore one object of the present invention to provide for an efficient steering system for a vehicle which provides steering resistance to the hand-operated steering wheel in response to resistance of the road wheels. It is a further object of the present invention to provide for a vehicle steering system and method for steering the road wheels of a vehicle equipped with a steer-by-wire steering system. It is yet another object of the present invention to provide for a vehicle steer-by-wire steering system and method that does not require additional torque sensors and other components associated therewith to provide feedback to the hand-operated steering wheel.